1. Field of the Invention
This invention relates to a toner residual amount detection apparatus for use, for example, in a copying machine, a printer, a facsimile apparatus or the like for forming an image by the use of an electrophotographic process or an electrostatic recording process.
2. Related Background Art
In an image forming apparatus of the electrophotographic type such as a copying machine or a printer, an electrostatic latent image is formed on the surface of a photosensitive drum as an image bearing member, and the electrostatic latent image on the photosensitive drum is developed and visualized as a toner image by a toner carried on a developing sleeve as the developer carrying member of a developing apparatus. The toner image is then transferred to a transferring material, and the toner image is fixed on the transferring material by a fixing apparatus, and then the transferring material is outputted.
Many of conventional developing apparatuses provided in such image forming apparatuses adopt dry type development using a powder developer. FIG. 6 of the accompanying drawings is a schematic cross-sectional view showing an example of the conventional developing apparatus. This developing apparatus 100 has a rotatable developing sleeve 102 in the opening portion of a developing container 101 containing therein a toner t as a developer which is opposed to a photosensitive drum 107. Also, a rotatable feeding vane 104 for supplying the toner t to the developing sleeve 102 is provided near the developing sleeve 102 in the developing container 101 along the lengthwise direction of the developing sleeve 102.
During a developing operation, the developer carried on the developing sleeve 102 to which a developing bias is applied from a developing bias voltage 103 is carried out to the photosensitive drum 107 side at a developing position to thereby develop and visualize an electrostatic latent image on the photosensitive drum 107. As described above, during the developing operation, the toner t in the developing container 101 is carried out by the developing sleeve 102 and therefore, the toner t in the developing container 101 is decreased.
When the amount of the toner t in the developing container 101 becomes equal to or less than a predetermined level, the amount of the toner t carried out by the developing sleeve 102 is decreased and therefore, there occurs a state in which the quality of an output image is lowered by the occurrence of faulty developing.
Accordingly, to obviate the occurrence of such a state, a notice of a reduction in the toner residual amount for preventing faulty developing and a notice for demanding the supply of the toner t into the developing container 101 need be given when the residual amount level of the toner t has become equal to or less than a certain value, so that the residual amount of the toner t in the developing container 101 may not become equal to or less than a predetermined level. Also, when the notice of the reduction in the toner residual amount in the developing container 101 is ignored and an image forming operation is continued without any toner supply (or replenishment) being effected, it is necessary to further effect the stoppage of the image forming operation in order to prevent faulty developing, or the indication of a notice for demanding toner supply.
Therefore, heretofore, as shown in FIG. 6, an electrically conductive detecting member 105 for detecting the residual amount of the toner t has been provided in the developing container 101 near the developing sleeve 102 along the lengthwise direction of the developing sleeve 102, and a toner residual amount detecting portion 106 has detected the difference between a voltage induced in the detecting member 105 when a developing bias has been applied from a developing bias voltage source 103 to the developing sleeve 102 (hereinafter referred to as the antenna voltage) and a predetermined voltage value stored in the toner residual amount detecting portion 106 (i.e., a voltage value at which the residual amount level state of the toner t in the developing container 101 is a level at which “notice and replenishment are demanded”, and hereinafter referred to as the reference voltage), and from the result of this detection, the residual amount level state of the toner t in the developing container 101 has been detected.
That is, whether the residual amount level state of the toner t in the developing container 101 has lowered to the “notice and replenishment” level or not is detected by a change in the electrostatic capacity of a capacitor having the developing sleeve 102 and the detecting member 105 as pole plates.
Now, in the detection of the residual amount level state of the toner t in the developing container 101 in the above-described conventional developing apparatus 100, it is known that it can be reliably detected that the residual amount level state of the toner t in the developing container 101 has lowered to the level at which notice and replenishment are demanded, but as to whether the supply of the toner t has been done after this detection, erroneous detection is liable to occur.
As one of the causes of this erroneous detection, mention may be made of a change in the toner distribution (density) between the developing sleeve 102 and the detecting member 105. For example, when a transferring material is jammed during the image forming operation after the toner residual amount detecting portion 106 has lowered to the “notice and replenishment” level, if the developing apparatus 100 is dismounted from the image forming apparatus to effect the treatment thereof (hereinafter referred to as the jam treatment), the toner distribution between the developing sleeve 102 and the detecting member 105 as shown in FIG. 7A of the accompanying drawings will be destroyed by the vibration due to the shock or the like of the dismounting, as shown in FIG. 7B of the accompanying drawings, and the electrostatic capacity will be changed.
As a result, during the recovery or image forming after the jam treatment, a portion by which the antenna voltage exceeds the reference voltage will increase from the state of FIG. 8A of the accompanying drawings before the developing apparatus 100 is dismounted from the image forming apparatus, as shown in FIG. 8B of the accompanying drawings, and there will occur the phenomenon that in spite of the toner supply being not effected, the “notice and replenishment” display indicated on the panel of an operation portion (not shown) is turned off.
When such a phenomenon occurs immediately before the stoppage of the image forming operation, if the image forming operation is again continued after the above-mentioned “notice and replenishment” display, if an image having a high image percentage is to be formed, the supply of the toner t to the developing sleeve 102 has not been in time, and there has occurred the phenomenon that the formed image has a white blank area (hereinafter referred to as the blank image).
Also, in the above-described conventional toner residual amount detecting construction, when the surroundings of the developing apparatus have risen in temperature due to the heat generation in the image forming apparatus, there has been a case where similar erroneous detection occurs.
To avoid the phenomenon as described above, there becomes necessary the construction of an image forming apparatus which permits jam treatment to be effected without the developing apparatus being detached from the image forming apparatus, or an agitating mechanism or the like for uniformizing the toner distribution in the developing container after the developing apparatus is detached from the image forming apparatus and therefore, the image forming apparatus will suffer from a great increase in cost, complication and bulkiness, and this has hindered space saving and a lower cost.